/Engine/Source/Editor/UnrealEd/Public/EdMode.h
Lets each mode/tool handle frustum selection in its own way.
true if something was selected/deselected, false otherwise.
virtual bool FrustumSelect ( const [FConvexVolume](API\Runtime\Engine\FConvexVolume) & InFrustum, [FEditorViewportClient](API\Editor\UnrealEd\FEditorViewportClient) * InViewportClient, bool InSelect )